Better error reporting in parsing syntactic structures

src/syntactic_structure.py

@@ -86,7 +86,10 @@ class SyntacticStructure:
         for c in self.components:
             if c.idx == idx:
                 return c
-        raise RuntimeError("Unknown component id: {}".format(idx))
+        
+        cs = [c.idx for c in self.components]
+        msg = "Structure id={} has components: {}, but no component: {}".format(self.id, cs, (idx,))
+        raise RuntimeError(msg)
 
     def match(self, word):
         matches = self.components[0].match(word)